It is known that, in airplanes with mechanical controls, the stick directly controls an angle of deflection of the elevators, the amplitude of this angle being proportional to the swing of said stick. Thus, by acting on said stick, the pilot exerts a piloting action which momentarily positions the airplane about its center of gravity or which controls the attitude of said airplane. Such a piloting action is instinctive for the pilot.
It is also known that the electric flight controls, with which numerous modern airplanes are now equipped, make it possible to control an airplane by objective, that is to say to directly control a parameter, such as the load factor, by way of said stick, everything occurring as if the latter were graduated in terms of load factor. Such control is advantageous since, by graduating the stick in terms of load factor and by limiting the extent of controllable load factor, one is sure to preserve the integrity of the airplane in any maneuver whatsoever.
On the other hand, control in terms of load factor is not very instinctive for the pilot, since control in terms of load factor makes it possible to guide the airplane in the long term rather than to pilot it at an instant. Specifically, commanding a zero load factor amounts to prescribing a constant aerodynamic slope. By virtue of the stick, it is thus possible to guide the airplane by controlling its trajectory, thereby making it possible to easily use said electric flight controls either with a human pilot, or with an automatic pilot.
However, it results from the foregoing that, in very dynamic flight phases, for example in proximity to the ground, during which the control tasks are very short term, one is compelled to substitute with, for example said control in terms of load factor control in terms of rate of pitch.
Additionally, the known electric controls in terms of load factor cannot integrate protection of the airplane in terms of longitudinal attitude. It is therefore necessary to append thereto a supplementary attitude-based protection law and to interface the latter accurately with the electric flight control in terms of load factor, so as to avoid problems in proximity to the ground, such as touchdown of the tail (or tail-strike).
Moreover, it is also impossible to protect the airplane in terms of incidence solely through electric controls in terms of load factor. It is therefore necessary, here again, to add a supplementary incidence-based protection law and to undertake deft interfacing to avoid the risks of stalling of the airplane during standard maneuvers.